The objectives of the project are to evaluate the interaction of insulin and insulin-like growth factors (IGF) with the surface of endothelial cells and determine the effects of such surface interaction on endothelial cell functions. The endothelial cells, which line the internal surface of all blood vessels, were isolated from the arteries and veins of human umbilical cords and the pulmonary and systemic circulation of cows and maintained in culture. Such cultures of endothelial cells were shown to have specific receptors for insulin and specific receptors for one of the IGF, multiplication-stimulating activity (MSA). For insulin, the concentration of endothelial cell receptors was highly dependent on the vascular origin of the endothelial cell culture, with umbilical arterial endothelium having 2-5 times the receptor concentration as umbilical venous endothelial cells and bovine pulmonary arterial cells having three times the concentration of insulin receptors as pulmonary venous endothelium. All adult bovine endothelium had 4-10 times the concentration of EGF receptors as the human umbilical tissue. The role of these surface receptors for insulin and IGFs is being explored.